Thousands of people took to the streets of Manhattan on this Earth Day for the March for Science, celebrating science and demanding its protection.

Demonstrators lined up at Columbus Circle on Saturday morning, and marched down Broadway to Times Square.

Demonstrators said they are concerned about climate change, and are demanding the Trump administration invest in environmental efforts like cleaner air and water, and not defund them.

They said potential cuts to the Environmental Protection Agency would be a step backwards.

"I'm looking forward to a future in which we can solve problems that we have using scientific means," one protestor said. "And if we don't support our scientific organizations with government funding, in particular with education, we're not going to get anywhere, we're going to end up in a bad place."

"The Clean Air Act, the Clean Water Act, the Endangered Species Act — these are all things that came about after the very first Earth Day in 1970 — which is also today, coincidentally," said Bill Ulfelder, the executive director of the Nature Conservancy. "These are things that need to remain in place."

The city police department estimates about 40,000 people took part in the march.

Demonstrators across the country and world are also voicing support for scientific freedom.

The main march was held on the National Mall in Washington. Bill Nye, the Science Guy, was one of the main organizers of the event, and stressed science serves everyone.

"Today, we have a great many lawmakers — not just here, but around the world — deliberately ignoring and actively suppressing science," Nye said to the crowd at the nation's capital. "Their inclination in misguided and in no one's best interest. Our lives are in every way improved by having clean water, reliable electricity, and access to electronic global information."

More than 500 other cities held similar rallies. Thousands hit the streets in Los Angeles for a peaceful demonstration there.

And in London, people marched by the city's research institutions to push for future science funding.